An approximate theory for calculating the effect of volume occupancy upon biochemical equilibria and the rates of enzyme-catalyzed reactions has been outlined in previous reports. As reported earlier, this theory predicts that the equilibrium tendency of macromolecules to associate is greatly enhanced in solutions which are significantly volume-occupied. A recent extension of the theory shows that the increase in equilibrium association is due to a corresponding increase in the rate of association in volume-occupied systems, and that the rate of dissociation is little affected by volume occupancy. The equilibrium partition of macromolecules between mobile and stationary phases of a solution provides the physical basis for fractionation of molecules of chromatography. A new treatment of excluded volume effects in the sequestered (stationary) phase has led to an improved theory of equilibrium partitioning of concentrated protein solutions in size exclusion chromatography. The new theory accounts quantitatively for the observed concentration dependence of the partition coefficient of hemoglobin at concentrations of up to more than 200 g/l. Automated methods have been devised for measuring the molecular weight of macromolecules via sedimentation equilibrium and for measuring the sedimentation coefficient of macromolecules using any of several types of commonly available preparative ultracentrifuges in lieu of the conventional analytical ultracentrifuge. These methods have been tested using a variety of macromolecules and two different rotor geometries. The results, obtained with substantially less user effort and expertise than heretofore required, are in excellent agreement with literature values for both molecular weight and sedimentation coefficient.